Current technology limits the size of a single train methanol plant to about 5000 t/day. There is incentive to increase the scale of methanol production to enable economic conversion of remote natural gas into a transportable form, either for fuel needs or for other processes such as methanol-to-olefins (MTO) processes. Such prospects may entail increasing methanol production on a scale of from 2 to 4 times current processes.
Many methanol synthesis reactor designs currently utilize some sort of external cooling that takes place as the reaction proceeds. See Appl, M., Modern Production Technologies, British Sulphur Publishing, London, 1997 ISBN 1 8733387 26 1. Generally, the external cooling takes place in one of two ways: (i) several adiabatic reactor beds in series with coolers in between stages, or (ii) cooling tubes located within the fixed reactor bed. Either of these methods results in a relatively complicated reactor design due to the need for integrated cooling. The reactor feed must be preheated, and then additional heat transfer surface is required to remove the heat of reaction.
U.S. Pat. No. 5,512,599 discloses an ultra-large scale reaction apparatus capable of producing 5,000 tons/day or more of methanol. The methanol can be synthesized by means of a fluidized bed reactor at a linear velocity of 0.51 m/sec. The fluidized bed catalytic reactor includes internal heat transfer tubes.
U.S. Pat. No. 5,216,034 discloses the use of multiple reactors in series for making methanol. The reactors include catalyst in a fluidized bed. Each reactor is equipped with at least one heat exchanger, an inlet for synthesis gas and an outlet for the reaction mixture. Each outlet is connected to a heat exchanger, which is connected to a gas/liquid (methanol) separator. The separator has an outlet for unconverted synthesis gas, and the outlet is connected to the next reactor in series.
U.S. Pat. No. 4,956,392 discloses a process for producing methanol. Synthesis gas feed is passed through a fluidized bed catalytic reactor at a superficial linear velocity of at leat 0.2 m/sec. Heat is recovered from the reaction by passing a heat transfer medium though a heat transmission tube in the reactor.
U.K. Patent No. GB 2 202 531 discloses a process for producing methanol or mixed alcohol from synthesis gas using a fluidized catalyst bed. Catalyst particles in the bed are contacted with the synthesis gas at a superficial linear velocity of at least 0.2 m/sec and a pressure of 40 to 200 atmospheres. A heat transmission tube is installed in the reactor.
What is needed is a reaction system that substantially reduces or eliminates the need for integrated heat transfer within the reaction zone. Such a system would be particularly beneficial if it were uncomplicated in design, or had other such advantages as having limited quench points, a relatively even temperature profile, and/or a high degree of mixing. In addition, the system should be easily scaled to very large capacities.